1. Field of the Invention
The present invention relates to a color filter built in a liquid crystal display panel, a manufacturing method thereof, an active matrix type liquid crystal display provided with the color filter, and a manufacturing method thereof, and especially relates to a color filter, a manufacturing method thereof, an active matrix type liquid crystal display, and a manufacturing method thereof preferable for driving in IPS (In-Plane-Switching) mode.
2. Description of the Related Art
An active matrix type liquid crystal display is constituted by adhering two substrates together, and providing liquid crystal between them. FIG. 1A and FIG. 1B show a CF substrate in a conventional active matrix type liquid crystal display, and FIG. 1A is a schematic showing a pattern of color filters, and FIG. 1B is a schematic showing a pattern of a black matrix. FIG. 2 is a schematic of a TFT substrate in a conventional active matrix type liquid crystal display of IPS mode. FIG. 3A is a section view along an E-E line in FIG. 1 and FIG. 2, and FIG. 3B is a section view along an F-F line in FIG. 1 and FIG. 2.
A conventional liquid crystal display holds liquid crystal 103 between two substrates 101 and 102 as described above. Of the two substrates, color filters are formed on the substrate 101 as described later, and thin film transistors (TFT's) are formed on the other substrate 102 as described later. Generally, the substrate 101 is referred as a color filter substrate (CF substrate), and the substrate 102 is referred as a TFT substrate.
In the TFT substrate 102, gate electrodes 122 and common electrodes 123 extending in the horizontal direction are formed on a first transparent substrate 121. The common electrodes 123 include two linear parts 123a extending linearly in the horizontal direction, and connecting parts 123b extending in the vertical direction between the linear parts 123a, and mutually connecting the linear parts 123a in the pixels. Each of the connecting parts 123b is formed as shapes bending in the same direction at intermediate parts to turn the liquid crystal in two directions. An inter-layer insulating film 124 for covering the gate electrodes 122 and the common electrodes 123 is formed all over the surface.
An amorphous silicon layer 125 and an n+ amorphous silicon layer 126 are sequentially formed at positions aligned to the gate electrode 122 at an equal interval on the inter-layer insulating film 124. Also, data lines 127 extending vertically, pixel electrodes 128 placed in the pixels, drain electrodes 129, which are connected to the data lines 127 and extend to the n+ amorphous silicon layer 126, and source electrodes 130, which are connected to the pixel electrodes 128 and extend to the n+ amorphous silicon layer 126 on the inter-layer insulating film 124. The pixel electrode 128 includes two linear parts 128a extending linearly in the horizontal direction, and connecting parts 128b extending in the vertical direction between the linear parts 128a, and connecting the linear parts 128a each other. Each of the connecting parts 128b is formed as shapes bending in the same direction as the connecting parts 123b of common electrode 123 at intermediate parts to turn the liquid crystal in two directions. A passivation film 131 covering them is formed. An orientation film 132 is formed on the passivation film 131. A rubbing direction of the orientation film 132 is vertical as indicated by an arrow 133.
A polarization plate 134 is adhered on a rear side of the first transparent substrate 121.
The layers formed on the inter-layer insulating film 124 are indicated with a hatch pattern in FIG. 2.
In the CF substrate 101, a black matrix 112 is formed on a second transparent substrate 111. Rectangular openings 112a are formed at areas aligned to the pixel electrodes 128, or, in other words the center of pixels on the black matrix 112. Red color filters 113R, green color filters 113G, and blue colors filter 113B are arranged as stripes on the black matrix 112. Though the color filters are in contact with each other in the vertical and horizontal directions for simplicity in FIG. 1, color filters of the same colors are in contact with each other in the vertical direction, gaps are formed between filters of different colors, and they are not in contact with each other in the horizontal direction as shown in FIG. 3B.
Then, a flattening film 115 and an orientation film 116 for covering the color filters 113R, 113G, and 113B are formed sequentially. A rubbing direction of the orientation film 116 is vertical, and is the same as that of the orientation film 132.
A conductive layer 117 and a polarization plate 118 are adhered on a rear side of the second transparent substrate 111.
The conventional active matrix type liquid crystal display constituted in this way is driven in the IPS (In-Plane-Switching) mode. When a voltage applied to the data line 127 is transferred to the pixel electrode 128 through the drain electrode 129, the amorphous silicon layers 125 and 126, and the source electrode 130, electric field is generated between the pixel electrode 128 and the common electrode 123, and the liquid crystal 103 rotates. As the result, light emitted from a backlight (not shown) passes through the color filter, and colored light is emitted from the polarization plate 132. Since the connecting parts 123b and 128b have the shapes bending in the same direction, the liquid crystal 103 rotates in different directions above and below them. Thus, a yellowish image is hardly present when viewed in a tilted direction to a screen.
The color filter has various patterns. FIG. 4 shows a schematic of a conventional color filter pattern provided independently. In this conventional color pattern, color filters on neighboring pixels are separated in the vertical direction as well as the horizontal direction. The color filters of different colors 136R, 136G, and 136B are separated each other, and the color filters of same colors are separated as well.
There is twisted nematic (TN) type in addition the IPS mode among the active matrix type liquid crystal displays. FIG. 5 shows a schematic for a TFT substrate in a conventional active matrix type liquid crystal display of the TN mode. FIG. 6A is a section view along an I-I line in FIG. 5, and FIG. 6B is a section view along a J-J line in FIG. 5. For the liquid crystal display of TN mode shown in FIG. 5 and FIG. 6, constituting elements equivalent to those in the liquid crystal display of IPS mode shown in FIG. 2 and FIG. 3 have the same numerals, and are not provided with detailed descriptions.
A common electrode 140 is formed between the flattening film 115 and the orientation film 116 in CF substrate 101 of TN mode. The conductive film 117 is not formed on the rear side of second transparent substrate 111, and the polarization plate 118 is directly adhered. The common electrode 123 is not formed on the first transparent substrate 121, and rectangular plate-like pixel electrodes 141 are formed on the passivation film 131 in TFT substrate 102. The pixel electrode 141 is connected to the source electrode 130 through a contact hole 142 formed on the passivation film 131.
In the conventional liquid crystal display, the entire light which reaches the color filter substrate is not emitted outside, and a part of it is reflected by the color filter, and another part of it is reflected by the black matrix. The reflected light enters the amorphous silicon layer constituting the TFT. FIG. 7 is a schematic section view showing the light coming into the amorphous silicon layer. As shown in FIG. 7, the reflected light 137 from the color filter, and the reflected light 138 from the black matrix comes into the amorphous silicon layer 125, and photocurrent flows in the amorphous silicon layer, thereby fluctuating characteristic of the amorphous silicon layer as the result. FIG. 8 is a chart showing the fluctuation of TFT characteristic.
By design, it is assumed that a relation between gate voltage Vg and drain current Id (TFT characteristic) shown in a solid line is obtained, and OFF voltage is set as negative voltage providing the minimum value of drain current Id, and ON voltage is set as appropriate positive voltage. As the operation time extends, the TFT characteristic fluctuates because of the cause described above. More specifically, a shift toward the positive direction of gate voltage Vg is present as indicated by a broken line in FIG. 8. As the result, the gate current Id at OFF voltage increases, and the gate current Id at ON voltage decreases. Thus, a predetermined brightness is not obtained at the pixels.
The fluctuation of characteristic of amorphous silicon layer depends on the intensity of light coming into it, and the intensity of light largely varies according to the reflectivity of color filter. For example, the reflectivity of green color filter is about 1.01, and the reflectivity of blue color filter is about 1.02 while the reflectivity of red color filter is assumed to be 1. When incident light is coming into the amorphous silicon layer for an extended period, the TFT characteristic varies according to the colors, thereby generating a problem such as residual image, color unevenness, and flicker.
A liquid crystal display including a heterochromatic three-layer structure as a color filter just above a TFT is proposed to prevent fluctuation of the characteristic of amorphous silicon layer constituting the TFT caused by reflected light reflected from a color filter substrate (Publication of unexamined patent application Ser. No. Hei 6-331975). FIG. 9 is a schematic sectional view showing a conventional CF substrate and liquid crystal around it where three layers of color filters are laminated on a part opposing to a TFT. A light-shielding film 151 is formed in an area opposing to the TFT on a transparent substrate 150, a red color filter 152R is formed in a red pixel area 155R, and a green color filter 152G is formed in a green pixel area 155G. A blue color filter 152B is formed on a blue pixel area (not shown) on the transparent substrate 150 as well. The red color filter 152R, the blue color filter 152B, and the green color filter 152G are laminated sequentially on the light-shielding film 151. The thickness of the color filters are about 1 μm, respectively.
With the liquid crystal display including this structure, the color filter absorbs most of the incident light into the color filter, thereby reducing reflected light coming into the amorphous silicon layer, resulting in restraining the fluctuation of TFT characteristic.
When the three-layer color filter is laminated in this way, a step of about 2 μm of a film thickness difference corresponding to two color layers (color filters) is generated between the laminated part and the center of pixel in the color filter substrate. When this step is generated, liquid crystal 153 is aligned along a wall of the step, thereby generating an uneven alignment direction. As the result, light 154, which is not intended to pass, passes through a neighborhood of the wall of step.
A liquid crystal display where independent colored films are formed on pixels is proposed to provide high brightness by increasing the intensity of out-going light (Publication of unexamined patent application Ser. No. 2000-89248).
Though, for a liquid crystal display (LCD) with dot inversion driving, if a color layer with the same color is formed continuously at least at parts, a flicker is hardly recognizable since plus charge and minus charge of the color layer cancel each other, the plus charge and the minus charge do not cancel each other in a LCD as one disclosed in the Publication of unexamined patent application No. 2000-89248, where a color layer with the same color is formed separately, resulting in a strong flicker.